Electrical-communication-receiving apparatus



July 1, 1930. J. HERMAN 1,769,431

ELECTRICAL COMMUNICATION RECEIVING APPARATUS Filed May 28. 1928 INVENTOR JZZ eI num/ ATTORNEY Patented Julyl, 1930 JOSEPH HERMAN, F WESTFIELD, NEW' JERSEY, ASSIGNOR TO A'MERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK Application filed May 28,

The principal object of my invention is to provide a new and improved receiver in an electrical communication system that shall not be affected by certain interfering currents induced in the associated circuits. Another object of my invention is to provide a telegraph receiver that shall be unaffected by interfering currents of a particular frequency. Still another object ofmy invention is to m provide a two-terminal telegraph receiving unit that can be connected readily wherever a telegraph receiver is to be used and that shall be specially free from effects due to interfering currents of a particular frequency. These objects and various other objects of my invention will become apparent on consideration ofa'limited number of examples showing practice according to the invention. It will be understood that the following specification will relate more particularly to these examples, and that the scope of the invention will be indicated in the appended claims. Referring to the'drawings, Figure 1 is a diagram showing the use of my improved receiving apparatus in a polar duplex telegraph system, and Fig. 2 is a diagram showing its use in a normal closed circuit Morse system.

In Fig. 1, the line 11 may be subject to interference by induction from a neighboring power line 12.. At each end of the line 11 there is the usual equipment of polar duplexapparatus, indicated at the left in some detail and at the right symbolically by a box 13. The transmitting relay 14 determines the polarity of the transmitted current which divides to the two equal resistances 15, and to the line 11 and the artificial line 11 which 40 simulates the line 11. Accordingly, in transmission the two points 16 and 17 will be points of equal potential and there will be no efiect in the receiving relay X.

Currents transmitted from the apparatus 13 over the line 11 will divide, going partly through the receiving apparatus between the points 16 and 17 and partly through the resistances 15. Direct currents received from the line will be blocked by thecondensers G,

and hence will flow through the resistances 1928. Serial No. 281,140.

R and the receiving relay X between them.

t will be seen that between the points 16 and 17 there is a Wheatstone bridge, with a series combination of inductance L and capacity C in each of two opposite arms and with a resistance R in each of the other two opposite arms, and with the receiver X in the bridge. Each combination of capacity C and inductance L will be adjusted to be resonant at the frequency of the interfering v induction from 12, and each resistance R will be adjusted to equal the resistance component of the inductance Land capacity C at the resonant frequency. a 7

It will readily be seen that the bridge will be in balance for currents of the resonantfrequency so that they will have null efiect on the receiving relay X.

For other frequencies than the resonant frequency the bridge will be out of balance and the received currents will be effective in the receiving relay X.

The receiving apparatus between the points 16 and 17 in Fig. 1 may be regarded as areceiving unit adapted to be used as a receiver in any ordinary telegraph system, and adapted to be adjusted to give null effect for received currents of a particular frequency. In Fig. 2 I have indicated a normal closed circuit Morse system with a transmitting key at 21 with the associated switch 22 to be opened when transmitting at this station. The associated receiving apparatus at thisstation lies in the circuit between the points 16 and 17 and is the same as between the points 16 and 17 in Fig. 1 and operates in the same way. The impedance elements of the bridge between the points 16 and 17 may be adjusted the same as for Fig. 1 with respect to a particular interfering frequency of current so that it will have null effect onthe receiving relay X, but direct current impulses and currents of other frequencies will be effective on this relay.

I claim:

1. In combination, a line of a communication system subject to interfering currents of a certain frequency, a Wheatstone bridge connected to the line so as to impress received voltages across two of the'vertices of the said bridge, a receiving device connected across the other tWo vertices of the said'bridge, a se- V ries inductance-capacity combination in eachof two opposite arms of the said bridge, each u 's'aid combination beingresonant to currents oftheinterfering frequency, and a resistance in eachof the other two arms of the said bridge ofthe same valueas the resistance com- 7 ponento'f either inductance-capacity combination at resonance frequency, whereby the a said 'receiving-devicewill be in balance with respect to currents of the said interfering fre quency;

, 2. Electrical communication receiving apk 5 paratus to give'null effect for a particular I interfering frequency, consisting of a Wheatstone bridge with one pair of opposite arms Y resonantatthat frequency and With -resistances in theother two arms and with a receivingedev ice in the bridge. V c

3. Electrical.communication comprising a lineandreceiving apparatus to give null effect at a particular interfering frequency, consisting of a'Wheatstone-bridge and a re 2 ceiving device as the bridging element be tween two opposite Vertices thereof, the arms 'ofthe bridge comprisingv resonant combinal tions and adjusted for balance to receive sig-' naling impulses at the resonant frequency, v said line being connected to impress received voltages across the-remaining two opposite ertic'es'of the bridge v In testimony whereof, I have signed my name to this specification this 25th day of 3 May 1928.1 a

a g JOSEPH HERMAN. 

